1. Field of the Invention
The present invention relates to a rechargeable lithium battery.
2. Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as a power source for small portable electronic devices. They use an organic electrolyte solution and thereby have twice the discharge voltage of a conventional battery using an alkali aqueous solution, and accordingly have high energy density. For positive active materials of a rechargeable lithium battery, lithium-transition element composite oxides being capable of intercalating lithium such as LiCoO2, LiMn2O4, (0<x<1), and so on have been researched.
The negative active material may include various shapes of carbonaceous materials that are capable of intercalating/deintercalating lithium such as artificial or natural graphite, hard carbon, a metal-based material such as Si, or a lithium composite compound such as lithium vanadium oxide. The electrolyte solution is composed of a lithium salt such as LiPF6 or the like and an organic solvent. The requirements for an organic solvent are low reactivity with lithium; low internal resistance to facilitate the transferrance of lithium ions; thermal stability over a wide temperature range; compatibility with other battery constituent elements of a negative electrode, a positive electrode and the like, in particular, a negative active material; and a high dielectric constant for dissolving a large amount of lithium salt.
Representative examples of an organic solvent include a cyclic carbonate such as ethylene carbonate or the like, dimethyl carbonate, a linear carbonate such as diethyl carbonate or the like, 1,2-dimethoxyethane, diethoxyethane, and mixtures thereof. Recently, research for improving the low temperature characteristics have been conducted. For example, U.S. Pat. No. 5,639,575 discloses an electrolyte solution in which diethyl carbonate having good low temperature characteristics is added to ethylene carbonate/dimethyl carbonate. However, the low temperature characteristics are still not satisfactory.